Field of the Invention
The invention relates to a multilevel converter comprising at least two submodules connected in series, wherein each submodule has in each case at least two switches and a capacitor and two current-carrying external module terminals.
Such a multilevel converter is known for example from the document “An Innovative Modular Multilevel Converter Topology Suitable for Wide Power Range” (A. Lesnicar and R. Marquardt, 2003 IEEE Bologna Power Tech Conference, Jun. 23-26, 2003, Bologna, Italy). This previously known multilevel converter is a so-called Marquardt converter arrangement comprising at least two series circuits connected in parallel. Each of the series circuits connected in parallel comprises in each case at least two series-connected submodules comprising in each case at least two switches and a capacitor. The voltage level at the output of the multilevel converter can be set in a targeted manner by means of a suitable driving of the switches.
In the case of modular multilevel converters, the individual submodules at the present time are arranged in a manner electrically insulated from one another. On account of the electrical insulation, the current forces that occur during the operation of the submodules can bring about considerable mechanical vibrations which can subject the submodules as such, and the components connected thereto, to considerable mechanical loading and lead to premature ageing. In order to gain control of the problem of the vibrations that occur, nowadays additional mechanical damping devices are used in multilevel converters; however, said damping devices lead to considerable additional weight and can impair the insulation strength, under certain circumstances. Accordingly, the invention is based on the object of specifying a multilevel converter for which the vibration problem described is solved better than heretofore.